Normal saline solution, lactated Ringer's solution, etc., have been conventionally used as artificial cerebrospinal fluids for the purpose of replenishing cerebrospinal fluid (CSF) that is lost during neurosurgery. These artificial cerebrospinal fluids have also been used for irrigating and perfusing an operation site (intracerebroventricular irrigation or perfusion fluid) (see Non-Patent Documents 1 to 3). However, in cases where normal saline has been used for the above purpose, side effects such as headache, fever, cervical stiffness, etc., have been reported. Fever has also been reported with the use of other artificial cerebrospinal fluids.
Cerebral edema is known as a primary factor for higher post-operative morbidity or mortality in many intracranial surgeries (see Non-patent Document 4). For example, Elliott K. A. C. et al. conducted experiments using Solution A which contains sodium ion, potassium ion, calcium ion, magnesium ion, chloride ion, glucose, etc., and further a predetermined amount of bicarbonate ion, and Solution B which contains the same components as Solution A excluding bicarbonate ion, as irrigation fluids, respectively, and consequently suggested that the composition of the fluids is one of the factors associated with the development of cerebral edema after brain exposure in cats (see Non-Patent Document 5).
More specifically, Elliott reported that when the brain surfaces of cats were irrigated with Solution B and Solution A, significant vasodilation of the brain surface was observed with Solution A unlike with Solution B, and the pH of the brain surface was lowered with Solution A, whereas physiological pH was maintained with Solution B. Based on these findings, Eliott indicates the importance of the bicarbonate ion in the above irrigation fluid. However, Elliott does not suggest the composition of an irrigation fluid that can reduce the incidence of cerebral edema.
As described above, the irrigation fluid or perfusion fluid used in the neurosurgery presumably increase or have possibilities of increasing the incidence of post-operative cerebral edema. However, the relations between a composition of such irrigation fluid or perfusion fluid and cerebral edema have not been elucidated, and an irrigation fluid or perfusion fluid which can prevent cerebral edema from developing or reduce the incidence of the same has not yet been reported.    Non-Patent Document 1: Oka K. et al., “The significance of artificial cerebrospinal fluid as perfusate and endoneurosurgery”, Neurosurgery, 38: 733-736, 1996    Non-Patent Document 2: Pople I. K. et al., “The role of endoscopic choroid plexus coagulation in the management of hydrocephalus”, Neurosurgery, 36: 698-702, 1995    Non-Patent Document 3: Whang C. J. et al., “Successful treatment of ventricultis by continuous intraventricular irrigation with gentamicin solution”, Surg. Neurol., 2: 91-94, 1974    Non-Patent Document 4: Rasmussen T. et al., “Cortisone in the treatment of postoperative cerebral edema”, J. Neurosurg., 19: 535-544, 1962    Non-Patent Document 5: Elliott, K. A. C. et al., “Physiological salt solutions for brain surgery”, J. Neurosurg., 6: 140-152, 1949